Current methods of analyzing human ascites are imperfect in distinguishing cancer from benign diseases. Studies were undertaken to assess the feasibility of measuring CEA-activity in these fluids by a modified zirconyl-phosphate gel radioimmunoassay (RIA) as an aid to detection of cancer. These studies show that assay of the CEA or CEA-like material present in malignant effusions can be an adjunct to cytology in the detection of malignancy, particularly of colo-rectal or other gastrointestinal origin. Studies are in progress to characterize and distinguish the malignant and benign markers in ascites in order to improve the accuracy of the RIA. BIBLIOGRAPHIC REFERENCES: Assays of CEA-like Substances in Extravascular Fluids: Methodologic Considerations. HZ Kupchik, RP McCabe, MS Loewenstein, RA Rittgers. In: Oncodevelopmental Gene Expressions. Eds. WH Fishman and S Sell. pp. 573-576, Academic Press, Inc., New York, 1976. CEA Assay of Ascites and Pleural Effusions: An Adjunct to Cytology in the Detection of Malignancy. M.S. Loewenstein, R.A. Rittgers, H.Z. Kupchik, A.E. Feinerman, B.R. Marcel, and N. Zamcheck. Clinical Research 24:373A, 1976 (Abstract).